DIRECT IN-SITU MEASUREMENT AND SPATIO-TEMPORAL MAPPING OF SOUND SPEED IN ANNULAR GAS FOR ACOUSTIC DIAGNOSTICS OF OIL WELLS

Abstract

Accurate determination of annular liquid level and bottom-hole pressure in oil wells critically depends on reliable estimation of the acoustic wave propagation velocity in the annular gas. Conventional echometric techniques typically rely on tabulated sound speed values or empirically corrected estimates, which do not adequately account for real thermobaric conditions, gas composition variability, and gas–liquid interaction effects. As a result, these approaches often introduce systematic measurement errors.

This study proposes a digital echolocation-based methodology for direct in-situ measurement and spatio-temporal mapping of sound speed in annular gas under real operating conditions. The approach employs controlled acoustic burst excitation, high-resolution digital signal acquisition, and adaptive signal-processing algorithms. A physical and mathematical framework describing acoustic wave propagation in annular space with spatially and temporally varying sound speed is developed.

The methodology was validated through field trials conducted on four producing oil wells operating under low annular pressure, elevated acoustic noise, and pronounced gas–liquid interaction effects. Directly measured sound speed values ranged from 352.24 to 376.14 m/s, revealing substantial deviations from tabulated values. Stable liquid-level reflections were reliably identified at depths between 285.03 and 711.11 m, despite adverse operating conditions. The deviation of calculated bottom-hole pressure from reference data did not exceed ±1 bar.

The results demonstrate that direct sound speed measurement significantly enhances the accuracy and robustness of acoustic liquid-level determination and enables a transition from empirical echometry toward physically grounded, adaptive acoustic monitoring of annular conditions in oil wells.